CEN16FA224 · Cessna 320E E

The commercial pilot and crew were conducting aerial photography work under contract with the U.S. Department of Agriculture. Shortly after departure, the pilot noticed an engine vibration coming from the airplane's right side and returned to the departure airport to have a mechanic inspect the engine. The pilot called the company operator to notify the company's owner of the engine anomaly; the operator and the crew agreed that they would stop aerial photography work and return to the operator's base in Longmont, Colorado but that they would call the operator's base to provide an update on the mechanics' findings before departing; however, the operator received no further communications from the crew.

GPS data showed the airplane departing AEJ and then heading south in the opposite direction of the operator's base and overflying one aerial survey point near C24. The airplane maintained an altitude of between 11,300 and 13,000 ft mean sea level (msl) with a ground speed between 120 to 169 knots for most of the flight. The last two minutes of flight showed the airplane circling around C24 while decreasing in altitude and fluctuating in airspeed between 140kts and 98kts. During the last 3 minutes of the flight, the airplane was descending, and the groundspeed decreased from 141 knots to 98 knots, before increasing to 128 knots and then rapidly decreasing to 99 knots during a sharp, 90º left turn to the north. The last recorded parameter showed the airplane at 8,665 ft msl with a groundspeed of 99 knots.

Witnesses stated that the airplane was on a left base for the runway but did not appear to be correctly positioned or high enough for the pattern into the airport. One witness stated that the airplane appeared to yaw and then return to wings level while descending to the ground. One witness stated he saw the propellers turning; however, two witnesses reported that they did not hear engine sounds.

Flight control continuity was established from all control surfaces to the cockpit input controls. Left and right engine test-runs and examinations revealed no evidence of any preaccident mechanical malfunctions or failures that would have precluded normal operation. However, examination of the left and right propellers indicated that the engines were likely operating with low to no power at the time of impact. Additionally, both propellers had several indications consistent with operating near their low-pitch position and they were not in the feathered position, consistent with the engines not being shut down by the pilot. The flaps were set to the 10º position and the gear was up, consistent with an approach configuration.

The pilot's autopsy findings revealed that he had an enlarged heart and moderate coronary artery disease, which slightly increased his risk of impairment from a cardiovascular event. However, there was no evidence of recent or old ischemic damage to the heart muscle or evidence of pilot impairment or incapacitation. Therefore, it is unlikely the pilot's cardiovascular disease contributed to the accident.

Given the evidence, it is likely the engines experienced a loss of power and that the pilot subsequently lost airplane control during the descent to the airport for landing, which resulted in impact with terrain. The reason for the dual loss of engine power could not be determined based on available evidence.

Verbatim NTSB analysis and probable cause from the NTSB dataset